1. Technical Field
The embodiments described herein relate to a voltage detection circuit for use in a semiconductor memory device, and more particularly, to a bulk voltage detector.
2. Related Art
In general, a semiconductor memory device uses internal voltages having various potential levels. The internal voltages includes a bit line pre-charge voltage (VBLP), a peak-to-peak voltage (VPP), a bulk voltage (hereinafter, referred to as ‘VBB’), and the like.
The bulk voltage (VBB) is a voltage applied to a bulk of a semiconductor substrate and has a negative voltage level that is lower than a ground voltage (VSS). This can result in a voltage difference between the semiconductor substrate and a source of a cell transistor. The voltage difference is called a body effect and the threshold voltage of the cell transistor is increased by the body effect. The increase in the threshold voltage decreases a leakage current of a MOS (Metal Oxide Semiconductor) transistor. The increased threshold voltage also increases the cell data retention time, thereby improving the refresh characteristic of the memory device.
A detector for comparing whether the bulk voltage is higher or lower than a bulk voltage (VBB) at a target level, an oscillator for generating an oscillation periodic signal according to an output signal of the detector, and a pumping circuit for generating the bulk voltage (VBB) are required to generate the bulk voltage (VBB). In particular, the detector should also be designed to have high sensitivity so as to sense a minute change in the bulk voltage (VBB). The detector should also be designed to have a high voltage gain.
Further, fluctuations of PVT (Process, Voltage, and Temperature) should produce only a small fluctuation or a low skew of the bulk voltage (VBB). However, the skew is closely associated with the sensitivity of the detector. When the sensitivity of the detector is high, the skew of the bulk voltage (VBB) increases. As a result, there is a trade-off relationship between the sensitivity of the detector and skew of the voltage level.